Global solar tracking system

ABSTRACT

A system may include determination of whether solar tracking of a first period of time is to be performed in a first region of sky or in a second region of sky, determination of a target tracker position in a first coordinate system if the solar tracking of the first period of time is to be performed in the first region of sky, and determination of the target tracker position in a second coordinate system if the solar tracking of the first period of time is to be performed in the second region of sky. In some aspects, determination of the target tracker position in the second coordinate system includes subtracting 360° from an azimuth angle in the first coordinate system if the azimuth angle in the first coordinate system is between +180° and +360°, wherein the azimuth angle in the second coordinate system is determined to be equal to the azimuth angle in the first coordinate system if the azimuth angle in the first coordinate system is between 0 and +180°.

BACKGROUND

A solar collector may receive solar radiation (i.e., sunlight) and direct the solar radiation onto a photovoltaic (or, solar) cell. A “concentrating” solar collector may also convert the received solar radiation into a concentrated radiation beam prior to directing the radiation onto the solar cell. The cell, in turn, may generate electrical power based on photons of the received radiation.

A solar collector is designed to generate power in response to radiation which intercepts the solar collector within a certain range of incidence angles. Power generation typically drops significantly if incoming radiation deviates from the range of incidence angles. The range depends on the design of the solar collector, and typically narrows with increasing concentration factors. For example, in some solar collector designs providing approximately 500-fold concentration, the range of incidence angles providing suitable power generation extends only one degree from normal.

In operation, a solar tracker aligns a solar collector with a radiation source (e.g., the sun) such that incoming radiation intercepts the solar collector within its preferred range of incidence angles. According to some systems, a solar collector is associated with a central axis perpendicular to its reception surface, and the above-mentioned alignment consists of moving the solar collector so that the axis points directly toward the apparent position of the sun in the sky.

FIG. 1 illustrates apparent solar positions 100A-100D within sky 110. Each of solar positions 100A-100D corresponds to a different time of day. Solar positions 100A-100D vary in both azimuth angle and elevation angle. Horizon 120 may be defined as the 0 degree elevation angle, and any direction may be defined as the 0 degree azimuth angle. For locations north of the Tropic of Cancer, apparent solar positions 100A-100D are always in the southern part of the sky. For locations south of the Tropic of Capricorn, apparent solar positions 100A-100D are always in the northern part of the sky.

Solar tracker 200 includes support 210, alignment device 220 and alignment device 230. Alignment device 220 is mounted on support 210 and is coupled to alignment device 230. Alignment device 230 is coupled to solar collector 300. Alignment device 220 may be controlled to rotate solar collector 300 to a particular azimuth angle, while alignment device 230 may be controlled to rotate solar collector 300 to a particular elevation angle. Such operation may be intended to align axis 310 of collector 300 with an apparent solar position in sky 110.

For a typical solar tracker, the elevation angle cannot exceed 90 degrees and the azimuth angle range of movement is usually less than 360 (e.g., between 0 degrees and 355 degrees, 0 degree is North). Typically, these constraints are implemented by mechanical limit switches and intended to prevent damage to tracker 200 and/or collector 300 due to malfunctions. These constraints may also or alternatively take into account physical considerations such as a length of cables within and attached to tracker 200. However, in order for a tracker to be deployed globally, it needs to be able to move to any azimuth angle (e.g., from 0 to 360 degree).

FIG. 2 is a graph illustrating solar paths during several days of a particular year at a location between the Equator and the Tropic of Cancer. The 0 degree azimuth angle represents North (e.g., True North). For most of the year, an azimuth angle of solar tracker 200 is moved through range A of angles shown in FIG. 2. On some days (i.e., May 19, June 21, and July 24, as well as the days in between), the azimuth angle of the solar position passes through North. Even if a tracker is mechanically capable of a 360 degree (or more) range of azimuth movement, according to conventional solar tracking algorithms, the solar azimuth angle will change on these days from 0 degrees to 360 degrees around noon. A conventional solar tracking algorithm will treat this as a 360 degree change in azimuth angle and will cause tracker 200 to rotate reversely through almost a 360 degree azimuth angle to continue tracking.

Solar collector 300 delivers negligible power during the large azimuthal rotation described above. Such a rotation may also lead to excessive wear on the mechanical elements of solar tracker 200. Similar issues would arise if solar tracker 200 were located between the Equator and the Tropic of Capricorn.

Moreover, conventional solar tracking algorithms are also not suited for use at multiple global locations. For example, locations North of the Tropic of Cancer require a solar tracking algorithm for tracking in the Southern part of the sky and locations South of the Tropic of Capricorn require a different solar tracking algorithm for tracking in the northern part of the sky. Similarly, solar tracker 200 would require another solar tracking algorithm if located between the Equator and the Tropic of Capricorn and yet another solar tracking algorithm if located between the Equator and the Tropic of Cancer. Maintaining different tracking algorithms for solar trackers located in different parts of the world may be inefficient, costly, and prone to errors.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a solar tracking system.

FIG. 2 is a graph illustrating elevation and azimuth coordinates for various solar paths.

FIG. 3 is a flow diagram of a process according to some embodiments.

FIG. 4 is a graph illustrating elevation and azimuth coordinates for various solar paths according to some embodiments.

FIG. 5 is a block diagram of a system according to some embodiments.

FIGS. 6A through 6C illustrate azimuth angular movement of a solar tracker according to some embodiments.

FIG. 7 is a flow diagram of a process according to some embodiments.

FIG. 8 is a perspective view of a solar collector array according to some embodiments.

DESCRIPTION

The following description is provided to enable any person in the art to make and use the described embodiments and sets forth the best mode contemplated for carrying out some embodiments. Various modifications, however, will remain readily apparent to those in the art.

FIG. 3 is a flow diagram of process 400 according to some embodiments. Process 400 and all other processes described herein may be executed by one or more hardware and/or software elements, one or more of which may be located remotely from one another. Although described herein with respect to specific systems, these processes may be implemented and executed differently than as described. According to some embodiments, process 400 may be embodied in firmware and performed by a microcontroller executing the firmware.

Initially, at S410, it is determined whether solar tracking during a period of time is to be performed in a first region of sky or a second region of sky. The period of time may encompass the upcoming day, several upcoming days, or a portion of the upcoming day. According to some embodiments, the determination at S410 occurs during a time at which no appreciable light is available from which to generate electrical current (e.g., after dusk and before dawn). Embodiments are not limited thereto, as the determination may be performed at any time of day, and may be performed more than once per day. In a particular example, S410 is performed a few hours before dawn of the first day, and the determination relates to whether solar tracking during the first day is to be performed in a first region of sky or a second region of sky.

The first region of sky may be a portion of sky which does not include a particular direction (e.g., North), while the second region of sky may be a portion of sky which includes the particular direction. In this regard, the first region of sky and the second region of sky may include some common directions. Using the example of FIG. 2, the first region of sky may comprise a mostly-Southernly region extending from 70 degrees from North, through South (e.g., True South), to 300 degrees from North, and the second region of sky may comprise a Northernly region extending from 85 degrees from North, through North, to 270 degrees from North.

The determination at S410 may be performed based on any techniques that are or become known. According to some embodiments, S410 comprises determining the solar noon azimuth angle for the upcoming day. This determination may comprise receiving date and location data via a Global Positioning System (GPS) receiver, and determining the solar noon azimuth angle based on the date and location data and on ephemeris equations and/or ephemeris tables. If the noon azimuth angle is within the first region of sky, it is determined that solar tracking during the first day is to be performed in the first region of sky. If the noon azimuth angle is within the second region of sky, it is determined that solar tracking during the first day is to be performed in the second region of sky.

According to some embodiments, S410 comprises receiving date and location data as described above, and comparing the data with stored information indicating solar tracking regions corresponding to various dates and locations. For example, the information may indicate that solar tracking is to be performed in the first region on all dates for all locations North of the Tropic of Cancer, and that that solar tracking is to be performed in the second region on all dates for all locations South of the Tropic of Capricorn. The information may further indicate a date for all locations between the equator and the Tropic of Cancer at which the solar position changes from the first region to the second region, a date for all locations between the equator and the Tropic of Cancer at which the solar position changes from the second region to the first region, a date for all locations between the equator and the Tropic of Capricorn at which the solar position changes from the second region to the first region, and a date for all locations between the equator and the Tropic of Capricorn at which the solar position changes from the first region to the second region. Calculations of such “transition dates” based on location data are known in the art.

Flow proceeds to S420 if it is determined that solar tracking for the period of time is to be performed in the first region of sky. A tracker position in a first coordinate system is determined at S420. The tracker position includes an elevation angle and an azimuth angle intended to align a solar collector with the sun at a given time. According to some embodiments, a solar position at the given time is estimated using GPS data, ephemeris tables and tracking error data as is known in the art.

The first coordinate system may be a coordinate system through which a solar tracker may continuously track the sun over the first region of sky. In one example, the 0 degree azimuth angle corresponds to North and the first region of sky is the mostly-Southernly region described above with respect to FIG. 2. The first coordinate system may therefore include azimuth angles which encompass this mostly-Southernly region.

According to some embodiments, the first coordinate system includes azimuth angles within the range of 0 and 360 degrees. As seen from FIG. 2, a solar tracker capable of continuous movement through this range will also be capable of tracking the sun through the first region of sky corresponding to range A. Since a solar position determined according to conventional techniques includes an azimuth angle within the range of 0 and 360 degrees, the determination at S420 may simply comprise determining a solar position using conventional techniques.

Flow proceeds from S410 to S430 if it is determined that solar tracking for the period of time is to be performed in the second region of sky. At S430, a tracker position in a second coordinate system is determined.

The second coordinate system may be a coordinate system through which a solar tracker may continuously track the sun over the second region of sky. Continuing with the current example, the 0 degree azimuth angle corresponds to North and the second region of sky is the Northernly region corresponding to range B of FIG. 2.

As described above, a solar tracking algorithm which represents azimuth angle only in the first coordinate system (e.g., 0 to 360 degree) is unable to continuously track the sun over range B. FIG. 4 is an alternative representation of the solar paths of FIG. 2. More specifically, the azimuth angles of range B are depicted as mathematically-equivalent angles of range C. In the present example, the second coordinate system includes azimuth angles within the range of −180 and +180 degrees. As seen in FIG. 4, after transforming the azimuth angle from a first coordinate system (e.g., 0 to 360 degrees) to a second coordinate system (e.g., −180 to 180 degrees), the azimuth angle will change continuously in the second coordinate system to allow continuous tracking of the sun through the second region of sky corresponding to range C.

According to this example, the tracker position determined at S430 includes an azimuth angle in the range of −180 to +180 degrees. Some embodiments of S430 include determining a solar position including an azimuth angle within the range of 0 and 360 degrees according to conventional techniques. The determined azimuth angle is then converted to the second coordinate system. Under the present assumptions, determined azimuth angles between 0 degrees and 180 degrees require no conversion (i.e., because the second coordinate system includes this range of azimuth angles), and determined azimuth angles between 180 degrees and 360 degrees are decreased by 360 degrees in order to place them in the range −180 degrees to 0 degrees.

S420 (or S430, depending on the result of the determination at S410) may repeat throughout the day in order to update the tracker position and thereby track the sun across the first region (or second region) of sky.

In some embodiments, a tracker position is determined in a coordinate system that is different from the first or the second coordinate systems and is converted thereto as required by S420 or S430.

Embodiments are not limited to the specific coordinate systems or conventions (e.g., 0 degrees=North) described above. The table below summarizes first and second coordinate systems that may be employed for various first and second regions of sky and various “0 degree” directions. The table also specifies a method to convert an azimuth angle from each of the first coordinate systems to an associated second coordinate system. Embodiments are not limited to those represented in the table.

First coordinate Second coordinate First region Second region system (azimuth system (azimuth of sky of sky angle a) angle b) Conversion method Primarily Primarily 0° to 360° −180° to 180° If (a <= 180), b = a Southern Northern (0° is North) (0° is North) If (a > 180), b = a − 360 Primarily Primarily −180° to 180° 0° to 360° If (a > 0), b = a Southern Northern (0° is South) (0° is South) If (a < 0), b = a + 360 Primarily Primarily 0° to 360° −180° to 180° If (a <= 180), b = a Northern Southern (0° is South) (0° is South) If (a > 180), b = a − 360 Primarily Primarily −180° to 180° 0° to 360° If (a >= 0), b = a Northern Southern (0° is North) (0° is North) If (a < 0), b = a + 360 Primarily Primarily −90° to 270° −270° to 90° If (a <= 90), b = a Southern Northern (0° is East) (0° is East) If (a > 90), b = a − 360 . . . . . . . . . . . . . . .

As is evident from the previous description, process 400 may address the tracking discontinuity presented by conventional solar tracking systems located in the Tropics. Moreover, process 400 may be equally suited to application at locations North of the Tropic of Cancer or South of the Tropic of Capricorn. Of course, at these locations, S410 will always provide the same result (i.e., solar tracking will always occur in the first region of sky or always in the second region of sky) and the same coordinate system will always be employed.

FIG. 5 is a block diagram of system 500 according to some embodiments. System 500 may execute process 400 but embodiments are not limited thereto. In addition, embodiments are not limited to the elements and/or the configuration depicted in FIG. 5.

System 500 includes solar collector 510 and solar tracker 520. Solar collector 510 may comprise any system for receiving solar radiation that is or becomes known. In some embodiments, solar collector 510 comprises a concentrating solar collector for receiving solar radiation, concentrating the solar radiation, and directing the concentrated radiation onto a solar cell. Solar collector 510 may comprise solar sensors such as Normal Incidence Pyrheliometer (NIP) sensors in some embodiments. Solar collector 510 may comprise an array of individual solar collectors according to some embodiments.

According to the illustrated embodiment, solar collector 510 generates direct current in response to received solar radiation. Inverter 515 may receive the direct current and convert the direct current to alternating current. Any suitable inverter may be employed, including but not limited to an inverter employing a maximum power point tracking servo. Inverter 515 supplies the alternating current to intended load 525. Inverter 515 may not be required in some embodiments, such as those employing the aforementioned NIP sensors.

Intended load 525 may comprise any device, network, or combination thereof intended to receive power generated by solar collector 510. Intended load 525 may comprise a private or public power grid to which solar collector 510 provides power. Intended load 525 may be coupled to a dedicated motor or energy storage device to be supplied power by solar collector 510, and/or may comprise a general-purpose power grid.

Solar tracker 520 may comprise hardware and/or software for moving solar collector 510 with respect to a position in the sky. Some embodiments of solar tracker 520 comprise an azimuthal drive to move solar collector 510 in the azimuth rotational plane and an elevational drive to position solar collector 510 in the elevation rotational plane. Solar tracker 520 may comprise hydraulically-driven elements according to some embodiments. In some embodiments, solar tracker 520 operates to position solar collector 510 so that an axis thereof (e.g., a central axis normal to a receiving surface) points at a desired position in the sky. The desired position may comprise a position of the sun, but embodiments are not limited thereto.

Control unit 530 includes processor 532 and storage 534. Processor 532 may comprise one or more microprocessors, microcontrollers and other devices to execute program code according to some embodiments. In this regard, storage 534 stores control program 535 comprising executable program code. Processor 532 may execute the program code of control program 535 in order to operate system 500 according to one or more of the processes described herein. In some embodiments of control unit 530, some or all of storage 534 resides within processor 532.

Storage 534 also stores ephemeris tables 536 for determining solar positions (and resulting tracker positions) corresponding to various locations, dates and times. Determination of a solar position in some embodiments may be based on ephemeris tables 536 as well as on ephemeris equations embodied in program code of control program 535. Error correction data 537 may comprise data used to correct for tracking errors as currently or hereafter known.

GPS receiver 540 may receive date, time and location data from the GPS network. Systems according to some embodiments may implement additional or alternative systems to retrieve date, time and/or position data, including but not limited to radio and GPS-like systems. This data may be used in conjunction with ephemeris equations and/or ephemeris tables 536 to determine a solar position and a position of solar tracker 520 as is known in the art. Date/time information may be obtained in some embodiments from a battery-backed Real Time Clock (RTC) maintained within system 500. Location data can be determined using a portable GPS unit or online source during installation of system 500, which would further include manual input of thusly-determined location data into control unit 530.

FIGS. 6A through 6C illustrate ranges of angular movement according to some embodiments, but embodiments are not limited to the illustrated ranges. In some embodiments, a solar tracker such as solar tracker 520 is capable of azimuthal movement through the illustrated ranges.

FIG. 6A illustrates a 540 degree range (i.e., from −180 degrees to +360 degrees) of continuous azimuthal movement. Although 0 degrees is depicted as North, embodiments are not limited thereto. Such a range may allow a solar tracker to move continuously through two different azimuthal coordinate systems as described above. The 540 degree range may be implemented by putting two independent limit switches around an azimuth motor shaft with proper rotation reduction rate, by placing the limit switches on a slip-ring structure, or by other methods known to the art.

FIG. 6B illustrates continuous movement between azimuthal angles 0 degrees and 360 degrees of the 540 degrees shown in FIG. 6A. The FIG. 6B movement may provide continuous tracking within a first coordinate system (i.e., 0 degrees through 360 degrees) as described with respect to process 400. Similarly, FIG. 6C illustrates continuous movement between azimuthal angles −180 degrees and +180 degrees of the 540 degrees shown in FIG. 6A. Movement between azimuthal angles −180 degrees and +180 degrees may provide continuous tracking within a second coordinate system (i.e., −180 degrees through +180 degrees) according to some embodiments.

FIG. 7 is a flow diagram of process 700 according to some embodiments. Process 700 may comprise an implementation of process 400, but embodiments are not limited thereto. Process 700 will be described below with respect to system 500 and particular directional conventions, but embodiments are also not limited thereto.

At S710, it is determined whether solar tracking for the upcoming day is to be performed primarily in the Northern sky or primarily in the Southern sky. Solar tracking is performed “primarily” in the Northern (or Southern) sky if the sun is in the Northern sky (or Southern) for the majority of daylight time. The determination at S710 may occur before dawn on the day in question. For example, the determination at S710 may be performed at 1 a.m. local time in some embodiments.

According to some embodiments, S710 comprises determining the solar noon azimuth angle for the upcoming day. It is determined that solar tracking for the upcoming day is to be performed in the Northern sky if the determined noon azimuth angle is in the Northern sky, and it is determined that solar tracking for the upcoming day is to be performed in the Southern sky if the determined noon azimuth angle is in the Southern sky.

As described with respect to S410, the determination of S710 may alternatively be based on stored information indicating that solar tracking is to be performed in the Southern sky on all dates for all locations North of the Tropic of Cancer, and that that solar tracking is to be performed in the Northern sky on all dates for all locations South of the Tropic of Capricorn. The stored information may also specify the above-described transition dates for locations between the equator and the Tropic of Cancer and for locations between the equator and the Tropic of Capricorn. In some embodiments, these dates are calculated on-the-fly during process 700.

A software flag is set to NORTH or SOUTH at S710 depending on the result of the determination. Flow then pauses at S720 until the upcoming day begins. In some embodiments, the day is determined to begin when the sun is at a first position from which light can be received and converted to electrical current. This position may vary depending upon the solar collector used in conjunction with process 700.

Process 700 may be initiated upon initialization of a system according to some embodiments. For example, after installing a solar tracker and a solar collector during daylight of a particular day, S710 may be performed to determine whether solar tracking for the particular day is to be performed primarily in the Northern sky or primarily in the Southern sky. Since the particular day has already begun, flow then proceeds from S720 to S730.

A target tracker position is determined at S730. The target tracker position includes an elevation angle and an azimuth angle intended to align a solar collector with the sun. According to some embodiments of S730, a solar position is estimated using GPS data from GPS receiver 540, ephemeris tables 536 and error correction data 537 as is known in the art, and the target tracker position is determined to be equal to the solar position.

According to some conventional techniques, the target tracker position includes an azimuth angle between 0 degrees and 360 degrees, with 0 degrees being assigned to True North. The range of azimuth angles and the actual direction associated with each angle may differ from the present example.

Next, at S740, it is determined whether the software flag is set to SOUTH. The 0 degree to 360 degree azimuth coordinate system mentioned at S730 and illustrated in FIGS. 4 (i.e., range A) and 6B is intended, according to the present example, to allow continuous tracking of solar positions located primarily in the Southern sky. Therefore, since the software flag is set to SOUTH and the determined azimuth angle is between 0 degrees and 360 degrees, the solar tracker is moved at S750 to the determined target tracker position (i.e., to the determined azimuth angle and elevation angle).

S750 may comprise transmitting appropriate commands from control unit 530 to solar tracker 520 to ensure alignment of a central axis of solar collector 510 with the determined target tracker position. Such commands may include commands to rotate to the determined azimuth angle and to the determined elevation angle.

System 500 may employ any technique to move solar tracker 520 to a tracker position that is or becomes known. Some systems operate in terms of “encoder counts” instead of angles and therefore convert desired azimuth (and elevation) angles to encoder counts. If the current azimuth count differs from the desired count (i.e., angle) by more than a certain error threshold, solar tracker 520 is moved in an appropriate direction until the current azimuth count matches the desired count. Control of the elevation angle may proceed similarly.

Alternatively, flow proceeds from S740 to S760 if it is determined that the software flag is not set to SOUTH. Such a determination indicates that solar tracking is to be performed primarily in the Northern sky. According to the present example, and as illustrated in FIG. 6C and FIG. 4 (i.e., range C), azimuth angles between −180 degrees and +180 degrees provide continuous tracking of solar positions located primarily in the Northern sky. Accordingly, the azimuth angle of the target tracker position determined at S730 (i.e., between 0 degrees and 360 degrees) is converted to an azimuth angle between −180 degrees and +180 degrees at S760.

The conversion at S760 may proceed according to any suitable technique. The conversion may depend upon the coordinate system in which the azimuth angle was determined at S730 (i.e., 0 degrees to 360 degrees in the present example) and the coordinate system to which the azimuth angle is to be converted (i.e., −180 degrees to +180 degrees in the present example). According to some embodiments of S760, the converted azimuth angle is equal to the azimuth angle determined at S730 if the azimuth angle determined at S730 is between 0 degrees and +180 degrees. The converted azimuth angle is 360 degrees less than the azimuth angle determined at S730 if the azimuth angle determined at S730 is between +180 degrees and +360 degrees. For example, an azimuth angle of 120 degrees is converted to 120 degrees, while an azimuth angle of 310 degrees is converted to −50 degrees.

The solar tracker is then moved to the target tracker position at S750 as described above. If flow reaches S750 from S760, the target tracker position includes an elevation angle (e.g., between 0 degrees and 90 degrees) and an azimuth angle between −180 degrees and +180 degrees. According to some embodiments, solar tracker 520 might not be moved at S750 if the target tracker position is equal to or negligibly different from the current position of solar tracker 520. For example, solar tracker 520 may be moved at S750 only if at least one of the currently-determined elevation angle and azimuth angle differs from the corresponding angles of current position by 0.1 degree or more. Flow then proceeds to S770 to determine if daylight has ended.

If daylight has not ended, it is determined at S780 whether to update the target tracker position. S780 may be governed by a timer that indicates a period (e.g., 5 sec.) which should pass between tracker position updates. Flow returns to S730 once the period has ended. Flow proceeds directly from S770 to S730 in some embodiments to provide continuous execution of S730 through S760.

In the illustrated embodiment, flow cycles from S730 through S780 until an end of daylight is determined at S770. The end of daylight may represent a time at which the sun is no longer at a position from which light can be received and converted to electrical current. The end of daylight may be determined based on a comparison between the current time and any time indicating an end of daylight (e.g., dusk, twilight, astronomical twilight, etc.). The end of daylight may be determined based on the power output by system 500 in some embodiments.

Flow returns to S710 once the end of daylight is determined at S770. S710 may be performed again after a specified number of hours have elapsed and/or at a specific time after the end of daylight (e.g., 3 a.m. local time). Process 700 may then proceed as described above with respect to a next day. Although process 700 depicts setting a software flag to NORTH or SOUTH prior to the beginning of each day, embodiments are not limited thereto. Such a software flag may be set every few days, and/or may be predetermined for each calendar day (i.e., allowing S710 to be omitted from the daily process).

FIG. 8 is a perspective view of solar collector 800 according to some embodiments. Solar collector 800 may comprise an implementation of collector 510 and may generate electrical power from incoming solar radiation. Collector 800 may be mounted on a solar tracker such as solar tracker 520 to maintain a desired position relative to the sun during daylight hours.

Solar collector 800 comprises sixteen instantiations 810 a-p of concentrating solar collectors. Each of concentrating solar collectors 810 a-p may be connected in series to create an electrical circuit during reception of light by solar collector 800. Embodiments are not limited to the arrangement shown in FIG. 8.

As described in U.S. Patent Application Publication No. 2006/0266408, each of concentrating solar collectors 810 a-p includes a primary mirror to receive incoming solar radiation substantially parallel to axis 815 and a secondary mirror to receive radiation reflected by the primary mirror. Each secondary mirror then reflects the received radiation toward an active area of a solar cell within a corresponding one of collectors 810 a-p.

A perimeter of each primary mirror may be substantially hexagonal to allow adjacent sides to closely abut one another as shown. In some embodiments, a perimeter of each primary mirror is square-shaped. Each primary mirror may comprise low iron soda-lime or borosilicate glass with silver deposited thereon, and each secondary mirror may comprise silver and a passivation layer formed on a substrate of soda-lime glass. The reflective coatings of the primary and secondary mirrors may be selected to provide a desired spectral response to the wavelengths of solar radiation to be collected, concentrated and converted to electricity by collector 800.

Each primary mirror and secondary mirror is physically coupled to substantially planar window or cover glazing 820. Each of collectors 810 a-p is also to coupled to backpan 830. Backpan 830 may comprise any suitable shape and/or materials and may provide strength and heat dissipation to collector 800. The electrical current generated by each of concentrating solar collectors 810 a-p may be received by external circuitry coupled to backpan 830 in any suitable manner.

The several embodiments described herein are solely for the purpose of illustration. Embodiments may include any currently or hereafter-known versions of the elements described herein. Therefore, persons in the art will recognize from this description that other embodiments may be practiced with various modifications and alterations. 

1. A method comprising: determining whether solar tracking during a first period of time is to be performed in a first region of sky or in a second region of sky; determining a target tracker position in a first coordinate system if the solar tracking during the first period of time is to be performed in the first region of sky; and determining the target tracker position in a second coordinate system if the solar tracking during the first period of time is to be performed in the second region of sky.
 2. A method according to claim 1, wherein the determined target tracker position comprises an azimuth angle, the method further comprising: controlling a solar tracker to move to the determined target tracker position during the first period of time.
 3. A method according to claim 2, wherein the first region of sky is primarily a northern portion of sky with respect to the solar tracker, and wherein the second region of sky is primarily a southern portion of sky with respect to the solar tracker.
 4. A method according to claim 2, further comprising: determining a second target tracker position in the first coordinate system if the solar tracking during the first period of time is to be performed in the first region of sky; determining the second target tracker position in the second coordinate system if the solar tracking during the first period of time is to be performed in the second region of sky; and controlling the solar tracker to move to the determined second target tracker position during the first period of time.
 5. A method according to claim 4, further comprising: determining whether solar tracking during a second period of time is to be performed in the first region of sky or in the second region of sky; determining a third target tracker position in the first coordinate system if the solar tracking during the second period of time is to be performed in the first region of sky; determining the third target tracker position in the second coordinate system if the solar tracking during the second period of time is to be performed in the second region of sky; and controlling the solar tracker to move to the determined third target tracker position during the second period of time.
 6. A method according to claim 1, wherein determining the target tracker position in the second coordinate system comprises: determining an azimuth angle in the first coordinate system; and determining an azimuth angle in the second coordinate system based on the azimuth angle in the first coordinate system.
 7. A method according to claim 6, wherein the first coordinate system comprises azimuth angles between 0° and +360°, and wherein the second coordinate system comprises azimuth angles between −180° and +180°.
 8. A method according to claim 7, wherein determining the target tracker position in the second coordinate system comprises: subtracting 360° from the azimuth angle in the first coordinate system if the azimuth angle in the first coordinate system is between +180° and +360°, wherein the azimuth angle in the second coordinate system is determined to be equal to the azimuth angle in the first coordinate system if the azimuth angle in the first coordinate system is between 0° and +180°.
 9. A method according to claim 1, wherein determining whether solar tracking during the first period of time is to be performed in the first region of sky or in the second region of sky comprises: determining an azimuth angle of the sun corresponding to noon of the first period of time; determining that solar tracking during the first period of time is to be performed in the first region of sky if the azimuth angle of the sun corresponding to noon of the first day is within the first region of sky; and determining that solar tracking during the first period of time is to be performed in the second region of sky if the azimuth angle of the sun corresponding to noon of the first period of time is within the second region of sky.
 10. A method according to claim 1, wherein the determination of whether solar tracking during the first period of time is to be performed in the first region of sky or in the second region of sky is performed before dawn and after 12:01 a.m. of the first period of time.
 11. A method according to claim 1, wherein determining whether solar tracking during the first period of time is to be performed in the first region of sky or in the second region of sky comprises: determining a date on which a solar position changes between the first region of sky and the second region of sky.
 12. A system comprising: a solar tracker; and a control unit coupled to the solar tracker and to: determine whether solar tracking during a first period of time is to be performed in a first region of sky or in a second region of sky; determine a target tracker position in a first coordinate system if the solar tracking during the first period of time is to be performed in the first region of sky; and determine the target tracker position in a second coordinate system if the solar tracking during the first period of time is to be performed in the second region of sky.
 13. A system according to claim 12, wherein the determined target tracker position comprises an azimuth angle, the control unit further to: control the solar tracker to move to the determined target tracker position during the first period of time.
 14. A system according to claim 13, wherein the first region of sky is primarily a northern portion of sky with respect to the solar tracker, and wherein the second region of sky is primarily a southern portion of sky with respect to the solar tracker.
 15. A system according to claim 13, the control unit further to: determine a second target tracker position in the first coordinate system if the solar tracking of the first period of time is to be performed in the first region of sky; determine the second target tracker position in the second coordinate system if the solar tracking of the first period of time is to be performed in the second region of sky; and control the solar tracker to move to the determined second target tracker position during the first period of time.
 16. A system according to claim 15, the control unit further to: determine whether solar tracking of a second period of time is to be performed in the first region of sky or in the second region of sky; determine a third target tracker position in the first coordinate system if the solar tracking of the second period of time is to be performed in the first region of sky; determine the third target tracker position in the second coordinate system if the solar tracking of the second period of time is to be performed in the second region of sky; and control the solar tracker to move to the determined third target tracker position during the second period of time.
 17. A system according to claim 12, wherein determining the target tracker position in the second coordinate system comprises: determining an azimuth angle in the first coordinate system; and determining an azimuth angle in the second coordinate system based on the azimuth angle in the first coordinate system.
 18. A system according to claim 17, wherein the first coordinate system comprises azimuth angles between 0° and +360°, and wherein the second coordinate system comprises azimuth angles between −180° and +180°.
 19. A system according to claim 18, wherein determining the target tracker position in the second coordinate system comprises: subtracting 3600 from the azimuth angle in the first coordinate system if the azimuth angle in the first coordinate system is between +180°and +360°, wherein the azimuth angle in the second coordinate system is determined to be equal to the azimuth angle in the first coordinate system if the azimuth angle in the first coordinate system is between 0° and +180°.
 20. A system according to claim 12, wherein the determination of whether solar tracking during the first period of time is to be performed in the first region of sky or in the second region of sky comprises: determining an azimuth angle of the sun corresponding to noon of the first period of time; determining that solar tracking during the first period of time is to be performed in the first region of sky if the azimuth angle of the sun corresponding to noon of the first period of time is within the first region of sky; and determining that solar tracking during the first period of time is to be performed in the second region of sky if the azimuth angle of the sun corresponding to noon of the first period of time is within the second region of sky.
 21. A system according to claim 12, wherein the determination of whether solar tracking during the first period of time is to be performed in the first region of sky or in the second region of sky is performed before dawn and after 12:01 a.m. of the first period of time.
 22. A method according to claim 12, wherein the determination of whether solar tracking during the first period of time is to be performed in the first region of sky or in the second region of sky comprises: determining a date on which a solar position changes between the first region of sky and the second region of sky. 